gsl: add 2.4 (#5768)
gsl: add 2.4 (#5768)


matthiasdiener/spack,LLNL/spack,lgarren/spack,EmreAtes/spack,tmerrick1/spack,iulian787/spack,mfherbst/spack,skosukhin/spack,krafczyk/spack,EmreAtes/spack,lgarren/spack,mfherbst/spack,EmreAtes/spack,LLNL/spack,iulian787/spack,iulian787/spack,lgarren/spack,matthiasdiener/spack,skosukhin/spack,mfherbst/spack,skosukhin/spack,krafczyk/spack,iulian787/spack,krafczyk/spack,mfherbst/spack,EmreAtes/spack,LLNL/spack,EmreAtes/spack,LLNL/spack,krafczyk/spack,matthiasdiener/spack,mfherbst/spack,tmerrick1/spack,matthiasdiener/spack,lgarren/spack,tmerrick1/spack,matthiasdiener/spack,skosukhin/spack,iulian787/spack,krafczyk/spack,skosukhin/spack,tmerrick1/spack,tmerrick1/spack,lgarren/spack,LLNL/spack